Aussie invention eliminates piston rings

words - Jeremy Bass
Victorian company's ringless air-seal system could revolutionise combustion engine design

A Victorian company is working on a technology with potentially major implications for future petrol and diesel engine design.

Warrnambool-based engineering consultancy Dynex has come up with a piston design that eliminates the spring-metal ring traditionally used to form a seal between the piston and the wall of the combustion chamber.

“That’s long been seen as essential in maximising compression and combustion efficiency,” Dynex CEO Brian Trigg told

“But our work so far suggests otherwise – that an absolute seal isn’t that important, and eliminating the friction generated by the rings on the cylinder wall can have far-reaching effects on engine design on the whole.”

The key to the technology lies in the replacement of metal rings with “virtual rings” of air pressure, created by the movement of air through grooves in the side of the piston.

“We’ve found a kind of compromise where our design produces a good-enough seal while virtually eradicating the friction created by normal rings.”

With patents in place, Dynex is currently in talks with a number of big-name car-makers worldwide, pitching its technology as a breakthrough in boosting mechanical, volumetric and thermal efficiency levels.

It stands to cut fuel consumption, exhaust emissions and wear-and-tear by eliminating internal friction. It’s also working on a version for rotary engines.

While Dynex is developing the new piston design for incorporation into existing engine designs, it also opens the way for a complete conceptual overhaul, giving potential rise to lighter and more compact engines.

While conventional piston rings form an effective seal, the friction they generate absorbs some of the kinetic energy the engine is trying to create and turns it into unwanted heat energy.

This is a large part of the reason cars need cooling systems. Eliminating friction allows engines to run cooler. That makes for smaller, smarter cooling systems, cutting associate pumping losses and reducing engine mass.

How the ringless piston works:

In place of the rings, each piston has numerous small, angled grooves, semi-circular at their apex. With the small clearances between them, the movement of the piston creates high-speed eddies -- air pressure working like metal rings to cut leakage and loss during the compression and combustion strokes.  

“That means there’s no metal-to metal contact between the pistons or rotors and their mating cylinders or housings. Virtually no friction means the mechanism needs no lubrication and there’s no wear and tear on major components,” said Trigg.

There’s an important by-product here, too. Putting an “air cushion” around the periphery of the combustion chamber creates a stratified air-fuel charge – an injection profile that enriches the mixture in the centre of the chamber and leans it up towards the periphery.

It’s the ideal set-up to make the most of each spark, already used in advanced engines by the likes of Benz and BMW for the win-win it produces in boosting performance while cutting consumption and emissions.

Dynex has brought the technology to the proof-of-concept phase, in which virtual modelling of the “air-sealing” principle looks promising enough to get to work on the real thing.

The company is working up a horizontally-opposed (boxer) prototype engine with conventional ringed pistons, with a view to replacing them with the grooved ones.

“We’ve reached the point where we need to secure corporate backing to push the project through the development stage towards international commercialisation,” Trigg said.

“While it’s not possible to predict time to market until we achieve that, we’re confident it won’t take long.”

The Dynex piston design also has major implications beyond the consumer car market, he added.

 “We are optimistic there’ll also be good demand for the technology for aircraft and military applications.”

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Published : Monday, 23 December 2013
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